Excess fluid retention in a subject can take various forms and can have different causes. Clinically, this fluid retention is called edema and can be classified as systemic or pulmonary edema. Examples of systemic edema include excess fluid accumulation in a subject's lower limbs, sacral area, abdominal cavity, or other parts of the body that receive blood through the aorta. Pulmonary edema involves a build-up of extravascular fluid in or around a subject's lungs.
One cause of pulmonary edema is congestive heart failure (“CHF”), sometimes referred to simply as “heart failure.” Heart failure is a major health problem—it is estimated that 5 million people suffer heart failure in the United States alone and it is believed to be growing at an approximate rate of 550,000 new cases each year due to, among other things, overall demographic aging. CHF can be conceptualized as an enlarged weakened heart muscle. As CHF worsens, the impaired heart muscle results in poor cardiac output of blood. Consequently, pulmonary circulatory pressure increases resulting in fluid leakage into extravascular spaces, pooling therein. This fluid pooling affects compliance of lung and oxygen exchange. For this reason, pulmonary edema can be an indicator of worsening or decompensated CHF.
Pulmonary edema can present a medical emergency that requires immediate care. The outlook for pulmonary edema patients can be good if detected early and treated promptly. If left undetected, and consequently untreated, pulmonary edema can lead to extensive hospitalization and even death.